Systems of Equations 2x2's - Cool math Algebra Help Lessons

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Coolmath Algebra
Systems of Equations 2x2's Lesson 1 - Solving by Graphing (page 1 of 2)
---- This algebra lesson explains what a 2x2 system of equations is and shows how to solve them by graphing.

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Here's another one:

Graph them!

Well, it LOOKS like they intersect at ( -2 , 0 ). But, what if it's really
( -1.999 , 0.001 ) ?

We have to check to be sure!

the graph of x + 2y = -2 and 3x - 2y = -6 ... they appear to cross at ( -2 , 0 )

Yep! So, the answer is

TRY IT:

Solve by graphing:

This is a cool method for getting you to see what's going on. But, it has serious problems.

What if you get a graph like this?

the graph of two lines that cross at an indeterminate point

What's the answer?

Uh... ( - .4 , 2.3 ) ?
( - .41 , 2.29 ) ?

There's no way to tell.

So, unless the problem is designed to cross at a nice, clean point, the graphing method is pretty useless for solving systems.

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